Effect of external magnetic field on the instability of THz plasma waves in nanoscale graphene field-effect transistors

The instability of plasma waves in the channel of field-effect transistors will cause the electromagnetic waves with THz frequency.Based on a self-consistent quantum hydrodynamic model,the instability of THz plasmas waves in the channel of graphene field-effect transistors has been investigated with external magnetic field and quantum effects.We analyzed the influence of weak magnetic fields,quantum effects,device size,and temperature on the instability of plasma waves under asymmetric boundary conditions numerically.The results show that the magnetic fields,quantum effects,and the thickness of the dielectric layer between the gate and the channel can increase the radiation frequency.Additionally,we observed that increase in temperature leads to a decrease in both oscillation frequency and instability increment.The numerical results and accompanying images obtained from our simulations provide support for the above conclusions.

Greatly Enhanced Methanol Oxidation Reaction of CoPt Truncated Octahedral Nanoparticles by External Magnetic Fields

Tunable behavior in electrocatalysis by external multifields,such as magnetic field,thermal field,and electric field,is the most promising strategy to expand the theory,design,and synthesis of state-of-the-art catalysts and the cell in the near future.Here,a systematic investigation for the effect of external magnetic field and thermal field on methanol oxidation reactions(MOR)in magnetic nanoparticles is reported.For Co_(42)Pt_(58)truncated octahedral nanoparticles(TONPs),the catalytic performance in MOR is greatly increased to the maximum of 14.1%by applying a magnetic field up to 3000 Oe,and it shows a monotonical increase with increasing working temperature.The magnetic enhanced effect is closely related to the Co content of Co_(x)Pt_(100-x)TONPs.Furthermore,the enhancement effect under a magnetic field is more obvious for Co_(42)Pt_(58)TONPs annealed at 650℃.First-principle calculation points out that the magnetic fields can facilitate the dehydrogenation of both methanol and water by suppression of entropy of the electron spin and lowering of the activation barrier,where OH_(ad)intermediates on Co sites play a more important role.The application of magnetic fields together with thermal fields in MOR provides a new prospect to manipulate the performance of direct methanol fuel cells,which will accelerate their potential applications.

Effect of Superstrong Magnetic Fields on Nuclear Energy Generation Rate in the Crust of Neutron Stars

这篇论文显示出那超级强壮的磁场(例如那些磁铁艺术) 能在中子星的外壳中多次增加精力产生率。这结果无疑不仅影响冷却中子星和中子星观察的 X 光检查光明而且中子的进化担任主角。

Suppressing of humping bead using an external magnetic field in high-speed gas metal arc welding

During high-speed gas metal arc welding （GMAW）, the backward flowing molten jet with high momentum in the weld pool is considered to be responsible for the occurrence of humping bead. To suppress humping bead, an electromagnetic device is developed and coupled with the welding system. By adjusting the conditions of external magnetic field, forward electromagnetic force is obtained to reduce the momentum of the backward flow of molten metal in weld pool. Consequently, the humping bead can be suppressed by adjusting the external magnetic field. Bead-on-plate welding experiment was conducted on mild steel plates, and the influence of magnetic flux density on the arc deflection angle and weld bead quality is investigated. It is found that external magnetic field can remarkably adjust the momentum of backward flow jet and significantly improve the quality of weld bead.

Effect of heating rate on the densification of NdFeB alloys sintered by an electric field

This study introduces a novel method of electric field sintering for preparing NdFeB magnets. NdFeB alloy compacts were all sintered by electric fields for 8 min at 1000~C with different preset heating rates. The characteristics of electric field sintering and the effects of heating rate on the sintering densification of NdFeB alloys were also studied. It is found that electric field sintering is a new non-pressure rapid sintering method for preparing NdFeB magnets with fine grains at a relatively lower sintering temperature and in a shorter sintering time. Using this method, the sintering temperature and process of the compacts can be controlled accurately. When the preset heating rate in- creasing from 5 to 2000~C/s the densification of NdFeB sintered compacts gradHally improves. As the preset heating rate is 2000C/s, Nd-rich phases are small, dispersed and uniformly distributed in the sintered compact, and the magnet has a better microstructure than that made by conventional vacuum sintering. Also, the maximum energy product of the sintered magnet reaches 95% of conventionally vacuum sintered magnets.

Numerical analysis of external magnetic field for mitigating backward flow momentum in weld pool

The external magnetic field is applied to mitigating backward flow jet of molten metal in weld pool so that humping bead may be suppressed during high speed gas metal arc welding（GMAW）. Therefore, the external magnetic field distribution in workpiece is critical to understand the interaction mechanisms of the external magnetic field with molten metal flow. In this study, the steady state external magnetic field induced by excitation device is numerically analyzed by using the the finite element software ANSYS and the three dimensional static magnetic scalar method. The distribution of external transverse magnetic field By in workpiece and arc area is calculated, and the influence of excitation current and air-gap distance on the distribution of transverse magnetic field By has been discussed. The magnetic field distribution in workpiece is measured by using a Tesla-Meter and compared with the simulated result. It is found that both are in good agreement.

Effect of an external magnetic field on improved electroslag remelting cladding process

Obtaining a uniform interface temperature field plays a crucial role in the interface bonding quality of bimetal compound rolls.Therefore,this study proposes an improved electroslag remelting cladding(ESRC)process using an external magnetic field to improve the uniformity of the interface temperature of compound rolls.The improved ESRC comprises a conventional ESRC circuit and an external coil circuit.A comprehensive 3D model,including multi-physics fields,is proposed to study the effect of external magnetic fields on the multi-phys-ics fields and interface temperature uniformity.The simulated results demonstrate that the nonuniform Joule heat and flow fields cause a non-uniform interface temperature in the conventional ESRC.As for the improved ESRC,the magnetic flux density(B_(coil))along the z-axis is pro-duced by an anticlockwise current of the external coil.The rotating Lorentz force is generated from the interaction between the radial current and axial B_(coil).Therefore,the slag pool flows clockwise,which enhances circumferential effective thermal conductivity.As a result,the uniformity of the temperature field and interface temperature improve.In addition,the magnetic flux density and rotational speed of the simulated results are in good agreement with those of the experimental results,which verifies the accuracy of the improved ESRC model.Therefore,an improved ESRC is efficient for industrial production of the compound roll with a uniform interface bonding quality.

Effect of alternative magnetic field on the diffusion layer growth in Al/Zn couple

The influence of an alternative magnetic field on the growth of the diffusionlayer in Al-Zn diffusion couple was studied. The thickness of the diffusion layer was examined. Theresults show that the alternative magnetic field increases the thickness of the diffusion layer andthe effect increases with the intensity and frequency of the alternative magnetic field increasing. The growth of the diffusion layer obeys the parabolic rate law and the growth rateincreases with the application of the alternative magnetic field. This growth rate change ismanifested through a change in the frequency factor k_0 and not through a change in the activationenergy Q. The frequency factor k_0 for the diffusion layer growth with the alternative magneticfield is 5.03 cm^2/s and the one without the magnetic field is 3.84 cm^2/s.

Deconfinement Phase Transition with External Magnetic Field in the Friedberg-Lee Model

The deconfinement phase transition with external magnetic field is investigated in the Friedberg-Lee model. We expand the potentiM around the two locM minima of the first-order deconfinement phase transition and extract the ground state of the system in the frame of functional renormalization group. By solving the flow equations we find that the magnetic field displays a catalysis effect and it becomes more difficult to break through the confinement.

Preliminary experimental study on applicability of Lorentz force velocimetry in an external magnetic field

Lorentz force velocimetry(LFV) is a noncontact technique for measuring electrically conducting fluids based on the principle of electromagnetic induction. This work aims to answer the open and essential question of whether LFV can work properly under a surrounding external magnetic field(ExMF). Two types of Ex MFs with different magnetic intensities were examined: a magnetic field with a typical order of 0.4 T generated by a permanent magnet(PM) and another generated by an electromagnet(EM) on the order of 2 T. Two forces, including the magnetostatic force between the Ex MF and PM in the LFV, and the Lorentz force generated by the PM in LFV were measured and analyzed in the experiment. In addition,Ex MFs of varying strengths were added to the LFV, and the location of the LFV device in the iron cores of the EM was considered. The experimental outcomes demonstrate that it is possible for a LFV device to operate normally under a moderate Ex MF. However, the magnetostatic force will account for a high proportion of the measured force,thus inhibiting the normal LFV operation, if the Ex MF is too high.

Effect of external stress and bias magnetic field on transformation strain of heusler alloy Ni-Mn-Ga

The influence of external field(magnetic field and stress field) on the transformation strain of Ni 52.9- Mn 24.4Ga 22.7 single crystal were investigated and its mechanism was also discussed. When thermally martensitic transformation occurs, about 0.25% transformation strain is obtained which may be obviously enhanced to about 0.8% by a 6 000 Oe magnetic bias field. However, the strain decreases by the external compress stress loaded along the strain-measured direction. When the external compress stress and bias magnetic field are simultaneously applied, the transformation strain decreases with increasing the magnetic field, which is related to the rearrangement of the martensite variants influenced by the external field.

Numerical analysis of arc-droplet behavior in thin wire high current MAG welding with magnetic control

High efficiency welding has always been one of the hot research subjects at home and overseas. Aiming at the problem of unstable droplet rotating spray transfer process in 450 A thin wire metal active gas arc(MAG) welding, a three-dimensional arc-droplet coupled model is established in this paper on the base of fluid dynamics to conduct numerical analysis for droplet transfer behavior with external magnetic controlled MAG welding, and used high-speed camera system to verify the simulation results. The results indicate that without external magnetic field, the droplet is transferred by the way of rotating spray, the arc is changeable and the spatter is serious. The electromagnetic force accelerates the radial liquid beam rotation under direct current(DC) magnetic field, and increases the angle between liquid beam and welding wire axis. Meanwhile, the rotation frequency of the liquid beam reaches 400 Hz, the area of arc column and heat loss increase under DC magnetic field. Based on the alternating magnetic field, the arc is the “bell shaped”, the arc stiffness raises, its temperature achieves 26 000 K, and the maximum speed of the liquid stream beam can reach 500 m/s. And the droplet transfer is more stable, the spatter significantly reduces, and welding quality is effectively improved.

LARGE TIME BEHAVIOR OF GLOBAL STRONG SOLUTIONS TO A TWO-PHASE MODEL WITH A MAGNETIC FIELD

In this paper,the Cauchy problem for a two-phase model with a magnetic field in three dimensions is considered.Based on a new linearized system with respect to(c−c_(∞),P−P_(∞),u,H)for constants c_(∞)≥0 and P_(∞)>0,the existence theory of global strong solution is established when the initial data is close to its equilibrium in three dimensions for the small H^(2) initial data.We improve the existence results obtained by Wen and Zhu in[40]where an additional assumption that the initial perturbations are bounded in L^(1)-norm was needed.The energy method combined with the low-frequency and high-frequency decomposition is used to derive the decay of the solution and hence the global existence.As a by-product,the time decay estimates of the solution and its derivatives in the L^(2)-norm are obtained.

The Study of Two Geomagnetic Jerks in China

This paper analyzes the first differences of the annual means (annual rate) for the Y and Z components of the geomagnetic field from nine magnetic observatories in China, measured from 1985 to 2003. The 1991 jerk was obvious in the Y component measured but not clear for the Z component. Rapid changes in the Z components were ubiquitous around 2000-2001, but not seen for the Y component. External effects were removed from the monthly means by comparing the monthly mean of the geomagnetic field components at the observatories with the monthly time series of the A_p geomagnetic index. However, some examples were analyzed and showed whether external effects were removed or not, there was no marked distinction in determining the jerks in China for the Y component and the Z component of the geomagnetic field. Finally, the isolines of the first differences of the annual means were used to analyze the spatial and temporal distributions of the jerks.

Explanation of Magnetic Destruction of Superconductor Using Schrodinger Equation in the Energy Space

The Wave function of Schrodinger Equation is expressed in terms of time dependent energy eigen function and spatial dependent wave function in the energy space, which gives spatial energy probability. This equation is utilized to find quantum momentum dependent on temperature. This in turn is used to find quantum complex resistance. This expression shows that the superconducting resistance vanishes for temperatures less than a certain critical value. This result conforms to superconductor conventional theory and empirical relations. The application of external magnetic field destroys superconductivity when its strength exceeds a certain critical value. The expression of the relationship between the critical magnetic field and the critical temperature is typical to the conventional one. This is the first time to obtain the conventional relationship for the superconductor’s resistance and critical magnetic field in one model in the energy space.

Quantum Correlations in Ising-XYZ Diamond Chain Structure under an External Magnetic Field

We consider an entangled Ising-XY Z diamond chain structure. Quantum correlations for this model are inves- tigated by using quantum discord and trace distance discord. Quantum correlations are obtained for different values of the anisotropy parameter, magnetic field and temperature. By comparison between quantum correlations, we show that the trace distance discord is always larger than quantum discord. Finally, some novel effects such as increasing the quantum correlations with temperature and constructive role of anisotropy parameter, which may play to the quantum correlations, are observed.

Lattice Boltzmann Simulation of Magnetic Field Effect on Electrically Conducting Fluid at Inclined Angles in Rayleigh-Bénard Convection

The magneto-hydrodynamics(MHD)effect is studied at different inclined angles in Rayleigh-Bénard(RB)convection inside a rectangular enclosure using the lattice Boltzmann method(LBM).The enclosure is filled with electrically conducting fluids of different characteristics.These characteristics are defined by Prandtl number,Pr.The considered Pr values for this study are 10 and 70.The influence of other dimensionless parameters Rayleigh numbers Ra=10^(3);10^(4);10^(5);10^(6) and Hartmann numbers Ha=0,10,25,50,100,on fluid flow and heat transfer,are also investigated considering different inclined anglesφof magnetic field by analyzing computed local Nusselt numbers and average Nusselt numbers.The results of the study show the undoubted prediction capability of LBM for the current problem.The simulated results demonstrate that the augmentation in heat transfer is directly related to Ra values,but it is opposite while observing the characteristics of Ha values.However,it is also found thatφhas a significant impact on heat transfer for different fluids.Besides,isotherms are found to be always parallel to the horizontal axis at Ra=10^(3) as conduction overcomes the convection in the heat transfer,but this behaviour is not seen at Ra=10^(4) when Ha>25.Furthermore,at Ra=10^(6),oscillatory instability appears but LBM is still able to provide a complete map of this predicted behavior.An appropriate validation with previous numerical studies demonstrates the accuracy of the present approach.

Magnetic Field Design by Using Image Effect from Iron Shield

Permanent magnet rings are presented, which exploit the image effect in the surrounding circular iron shields. The theory is given for a general permanent ring when the magnetization orientation at each coordinate angle ψ changes by =(n+1)ψ, where n is a positive or negative integer. For the uniformly magnetized case n=-1, the permanent ring produces no field in its bore, and the field is that of a dipole outside. When the ring is surrounded by a soft iron shield, its field becomes uniform in the bore, and zero outside the ring. The field can be varied continuously by moving the iron shield along the magnet axis. A small variable field device was constructed by using NdFeB permanent rings, which produced a field flux density of 0-0.5 T in the central region.

Effects of ultra-strong magnetic field on electron capture rates of^(55)Co and ^(56)Ni in the magnetar surrounding

The electron capture rates of 55Co and 56Ni in the ultra-strong magnetic field at four typical temperature- density points have been calculated using the nuclear shell model and Landan energy levels quantized approximate correction. The results show that the electron capture rates of 55Co and 56Ni are increased greatly in the ultra-strong magnetic field, and even exceed two orders of magnitude in the range from 4.414×10^13G to 2.207×10^27 G. The change rate of electron abundance, ye, of 55Co and 56Ni under the condition of B=4.414×10^15G in the magnetar surrounding has been calculated and discussed, the proportions of ye of 55Co and 56Ni in the total Ye have been reduced by 50 percent in all more than the condition without a magnetic field.